Negative-positive, positive-positive exposure station

ABSTRACT

An exposure station is provided for making both negativepositive and positive-positive electrophotographic prints without employing reverse development techniques to develop one of the images. This is accomplished by projecting an image of a negative original onto a photoconductive-liquid crystal sandwich structure across which a potential is applied to form a temporary image in the liquid crystal, which temporary image is the reverse of the negative original. This temporary image is then projected onto a charged photoconductive surface to form a positive electrostatic latent image. In the positive-positive mode the same light source can be used in a first embodiment to project an image of a positive original through the photoconductive-liquid crystal sandwich, when in its transparent state, onto the photoconductive surface. In a second embodiment a separate light source can be used for projecting an image of the positive original to form a positive electrostatic latent image on the charged photoconductive surface. In addition, control means is provided to assure that the image of only one original can be projected at a time. In a third embodiment a single light source is used for both the negative-positive mode and the negative-negative mode.

United States i Fields 1 1 NEGATIVE-POSITIVE, POSITIVE-POSITIVE EXPOSURESTATION Gary D. Fields, Parker, C010.

[73] Assignee: Eastman Kodak Company,

Rochester, NY.

[22] Filed: Feb. 17, 1972 [21] Appl. No.: 227,239

[75] Inventor:

Primary ExaminerRobert P. Greiner Artorne \'w. H. J. Kline et al.

[57] ABSTRACT An exposure station is provided for making bothnegative-positive and positive-positive electrophotographic printswithout employing reverse development techniques to develop one of theimages. This is accomplished by projecting an image of a negativeoriginal onto a photoconductive-liquid crystal sandwich structure acrosswhich a potential is applied to form a temporary image in the liquidcrystal, which temporary image is the reverse of the negative original.This temporary image is then projected onto a charged photoconductivesurface to form a positive electrostatic latent image. ln thepositive-positive mode the same light source can be used in a firstembodiment to project an image of a positive original through thephotoconductive-liquid crystal sandwich, when in its transparent state,onto the photoconductive surface. In a second embodiment a separatelight source can be used for projecting an image of the positiveoriginal to form a positive electrostatic latent image on the chargedphotoconductive surface. In addition, control means is provided toassure that the image of only one original can be projected at a time.In a third embodiment a single light source is used for both thenegative-positive mode and the negative-negative mode.

17 Claims, 3 Drawing Figures are-1111:

0R m;- asszsn PATENTED 39251973 sum 10F 3 I GARY o. FIELDS mvsmon.

0 BY Z of M ATTORNEYS ATTORNEYS i i 4 65H FIG 3 N (J :3 [Film "HH-Iggy-I GARY 0. FIELDS m INVENTOR.

BY 9 gm ATTORNEYS NEG ATIVE-POSITIVE, POSITIVE-POSITIVE EXPOSURE STATIONBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an exposure station, and more particularly to an exposurestation for an electrophotographic apparatus in which positive printscan be made from either a negative original or a positive originalwithout the use of reverse development techniques for developing one ofthe images.

2. Description of the Prior Art Toward the end of the 19th Century, F.Reinitzer and O. Lehmann independently observed that certain substancesin passing from a solid crystalline state to an isotropic liquid statepass through a state or condition over a given temperature range whereinthey display rheological properties similar to that of fluids, but haveoptical properties similar to that of the crystalline state. In order toidentify these properties, Lehmann used the term liquid crystal", whichterminology persists today. Present thinking tends to regard substanceswhich exhibit these properties as being in a fourth state of matterknown as the mesomorphic state or mesophase since it is a state or phaseintermediate that of the anisotropic crystal and that of the isotropicliquid.

There are three distinct mesomorphic states or forms, namely, thesmectic mesophase, the nematic mesophase and the cholesteric mesophase.A nematic liquid crystal is essentially transparent, and thereforetransmits light, but when placed in a d.c. electric field the moleculesof some of these liquid crystals become disoriented so that the materialdiffuses light and becomes milky white in appearance. When the dc.electric field is removed, the molecules of the liquid crystal return totheir previous orientation so that the liquid crystal is againtransparent. This phenomena is discussed in PROCEEDINGS OF THE I.E.E.E.,for July, 1968, in an article entitled: Dynamic Scattering: a NewElectro-optical Effect in Certain Classes of Nematic Liquid Crystals",by Heilmeier, Zanoni and Barton at pages l,l62-l,17l.

The reflective optical storage effect of mixtures of cholesteric andnematic liquid crystal materials is discussed in a paper appearing inAPPLIED PHYSICS LETTERS for Aug. 15, 1968 in an article entitled, A NewElectric Field Controlled Reflective Optical Storage Effect inMixed-Liquid Crystal Systems, by Heilmeier and Goldmacher at pages 132and 133, in which the authors describe how a mixture of nematic andcholesteric mesomorphic materials serve as an optical storage under ad.c. or low frequency a.c. electric field, which changes the initiallytransparent material to a milky white light-diffusing material. Theliquid crystal material remains in the light-diffusing state uponremoval of the d.c. field. The mixture can be rapidly erased or changedback to a transparent state by the application of a high frequency a.c.signal greater than 700 Hz.

US. Pat. No, 2,892,380 to Baumann et al describes a schlieren-opticalsystem for amplifying the light intensity of an optically projectedimage. A multiple layer control cell, consisting of a liquid crystallayer and a photoconductive layer, is bounded by a pair of electrodeswhich are connected to a d.c. source. The liquid crystal layer is a typewhich has an electric Kerr effect. An electrically non-conductive mirroris arranged between the photoconductive and liquid crystal layers toprovide optical isolation between a light image and a secondary lightsource. The light image is rastered on the photoconductive layer so thatit becomes conductive in those areas where light strikes it. Thisproduces a nonhomogeneous electric field between the electrodescorresponding to the light image which results in local variations inthe index of refraction of the liquid crystal material corresponding tothe light image. Light from a secondary source is reflected from thenonconducting mirror surface in accordance with the image pattern on theliquid crystal and is projected onto a screen to form a visible image.

In a conventional electrophotographic system a photoconductive surfaceis uniformly charged, as by a corona charger, which surface is thenexposed to a pattern of radiation that dissipates the charge on thephotoconductive surface inthe exposed areas to form an electrostaticlatent image corresponding to the original image. This image may then bedeveloped by bringing it in contact with toner particles having a chargeof opposite polarity to that of the electrostatic latent image to form atoner image which can be transferred to a suitable receiver or fused tothe photoconductive surface, if it is to serve as a receiver. However,in order to make a positive electrophotographic copy from a negativeoriginal, such as negative microfilm, it is necessary to reverse developthe exposed photoconductive surface i.e., develop the discharged areasof the photoconductive surface rather than the charged areas. One way toaccomplish this is to charge the photoconductive surface to a polarityopposite that used in the positivepositive mode and provide adevelopment electrode behind the photoconductive surface to which a biaspotential, having a polarity opposite the polarity of the tonerparticles and the charge pattern, is applied so that the toner particlesare repelled from the charged area and attracted to the uncharged area.However, some photoconductive materials will not retain both a positiveand negative charge and therefore can only be charged one way. Forexample, selinium will hold only a positive charge whereas zinc oxideusually will hold only a negative charge. With such materials, reversedevelopment can only be accomplished by using toner of opposite polaritywith a development electrode. However, it is a very difficult and timeconsuming job to change toner. Also, in actual practice it has beenfound that reverse development techniques usually re- 'sult in a printof inferior quality as compared to a print made by direct developmenttechniques.

SUMMARY OF THE INVENTION In accordance with this invention an exposurestation is provided for forming a latent image on a photosensitivesurface from either a first original or a second original, which is thereverse of the first original, wherein the latent image is always thereverse of the first original and the same as the second original. Thisexposure station includes means for supporting the photosensitivesurface for exposure, means for forming a temporary image which is thereverse of the first original, means for supporting the first and secondoriginals, means for projecting an image of the first original onto thetemporary image forming means to form the reverse' image, means forprojecting the reverse temporary image onto the photosensitive surfaceto form a latent imagethereon which is the reverse of the firstoriginal, means for supporting the second original, means for projectingthe second original onto the photosensitive surface to form a latentimage which is the same as the second original, and means forselectively projecting an image of either the first or the secondoriginal.

More particularly, an exposure station is provided for forming apositive electrostatic latent image on a charged photoconductive surfacefrom either a positive original or a negative original. A negativeoriginal is projected, as by means of ultraviolet light, onto a layeredsandwich which includes in order: a first transparent electrode, aphotoconductive layer which is respon-.

sive only to ultraviolet radiation, a liquid crystal layer, and a secondtransparent electrode. Means are provided for applying a dc. potentialacross the electrodes when the photoconductive surface is exposed to anultraviolet radiation pattern corresponding to the negative original toform a reverse or positive image in the liquid crystal layer. Thistemporary image is projected by a white light source onto a chargedphotoconductive surface to form a positive electrostatic image thereonwhich can be toned or otherwise utilized. In one embodiment a positiveoriginal support is provided which may be moved to a position betweenthe white light source and the sandwich structure so that the positiveimage may be projected through the transparent sandwich structure whenno potential is applied thereacross so that the positive image isprojected onto the charged photoconductive surface to form a positiveelectrostatic image of the positive original. In another embodiment, asecond white light source is provided for projecting an image of apositive original directly onto the charged photoconductive surfacewithout passing through the sandwich structurev In this embodiment,'apivoted mirror is provided which is movable from a first position forreflecting the image of the temporary image onto the photoconductivesurface to a second position out of the projection path of the image ofthe positive original. In addition, in each embodiment means areprovided for selectively projecting an image of either the positiveoriginal or the negative original to form a positive electrostaticimage.

Thus, it can be seen that a positive electrostatic image can be formedon a charged photoconductive surface from either a positive or negativeoriginal so that a positive print can be made without the necessity ofemploying reverse development techniques.

Additional advantages of this invention will become apparent from thedescription which follows, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of oneembodiment of the invention wherein a single light source is used toproject a temporary image or an image of a positive original; v

FIG. 2 is a diagrammatic view of an alternative embodiment of theinvention wherein separate light sources are used to form a temporaryimage and to project an image of a positive original; and

FIG. 3 is a diagrammatic view of a further alternative embodiment havinga single light source.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with thisinvention, in the embodiment of FIG. 1, a negative original 2 may besupported by a pair of spaced supports 4 in a projection plane so thatthe image thereon is projected by the first radiation means, such asultraviolet lamp 6, through a lens system 8 onto dichroic mirror 10,which transmits white light but reflects ultraviolet light. Thus, mirror10 reflects the image onto a photoconductive-liquid crystal sandwichstructure S which includes in order: a first transparent electrode 12, aphotoconductive layer 14 which is sensitive to ultraviolet light, aliquid crystal layer 16 and a second transparent electrode 18. A d.c.potential source 20 is provided which can be applied across theelectrodes, as by switch 22 to create a field therebetween. In this way,a reverse temporary image can be created of original 2 on the liquidcrystal layer 16, as will be more fully explained below. The temporaryimage is then projected by a light source of another wave length, suchas a white light source 24, through field lens 26 and objective lens 28and through an aperture 30 onto plane mirror 32 where it is re flectedonto a photosensitive surface 34, such as a uni formly chargedphotoconductive layer supported on a conductive support 36. When lamp 24is used to project a temporary image, positive image support 38 ispivoted about pivot pin 40 in the direction of arrow 42 so as not tointerrupt radiation from lamp 24.

A suitable photoconductive material for photoconductive layer 14 ispoly-N-vinylcarbozole or triphenylamine dispersed in a polystyrenevehicle. The liquid crystal layer 16 may be a nematic mesophase. Onesuitable nematic material comprises 80 mol percent of Butylp-(p-ethoxyphenoxycarbonyl)-phenyl carbonate and 20 mol percent ofp-[N-(pmethoxybenzylidene)amino] phenyl acetate. This ma terial is amesophase between 42C and 52C. Another suitable material is made upone-third by weight of each of P-[(p-methoxybenzylidene)amino] phenylacetate; p-(p-methoxybenzylidene) amino butyrate; andp-(p-butoxybenzylidene) amino acetate which is a mesophase between 25Cand 55C. Still another suitable nematic material isN-(p-methoxybenzylidene)-pbutylaniline which is a mesophase between 17Cand 44C. Other suitable materials are listed on pp. l ll 3 of MolecularStructure and the Properties of Liquid Crystals by G. W. Grey (1962).

A suitable thickness for the liquid crystal layer is 12 microns and isl0 microns for the photoconductive layer. The two layers convenientlyare separated by a layer of cellulose nitrate of 1 micron or less inthickness which layer is to inhibit adverse chemical reactions betweenthe liquid crystal material and the photoconductive material. In eachembodiment a potential of 250 to 400 volts across the electrodes issatisfactory.

When a positive original, such as original 44 is mounted in supports 45to be projected, ultraviolet lamp 6 is turned off and lamp 24 is used toproject an image of positive original 44 along a projection path throughlens 46, mounted on support 38, through dichroic mirror 10 andphotoconductive-liquid crystal sandwich S onto photoconductive surface34 to form a latent electrostatic image thereon. It will be understoodthat the images can be projected onto any photosensitive material butthat the invention has particular application for projection onto acharged photoconductive surface since in each case a positiveelectrostatic latent image is formed which can be toned by directdevelopment methods to form a positive toner image.

From the circuit logic shown in FIG. 1, it will be understood that if anegative original 2 is to be projected and is in the position shown,switch 48 will be closed to provide a signal to one input of AND gate50, which switch is connected to a potential source 52. A second signalto AND gate 50 when print button 54 is closed is provided from potentialsource 55. A third and final input to AND gate 50 is provided whenpositive original support 38 is swung in the direction of arrow 42 tothe dotted line position so that switch 56 is closed to supply a signalfrom potential source 57. When these positions are met AND gate 50 isenabled providing a signal to single shot 62 which in turn provides asignal of predetermined duration to ultraviolet lamp 6 to enable it andto solenoid 64 to close switch 22 thereby applying potential acrosstransparent electrodes 12 and 18 to provide an electric fieldtherebetween. If required, means, not shown, can be provided to vary theexposure time for originals of varying density. At the same time, thesignal from single shot 62 is provided to OR gate 66 which in turnprovides a signal to white light lamp 24. Thus, the image on negativeoriginal is projected onto photoconductive layer 14 which acts as thoughit is more conductive in those areas which are exposed to light therebyincreasing the electric field across corresponding portions of liquidcrystal layer 16 to form a temporary positive image in the liquidcrystal which is projected by means of white light 24.0nto generallyuniformly charged photosensitive surface 34 to form a positiveelectrostatic image which may be utilized in any well known manner. Upontermination of the signal from single shot 62 lamp 6 and lamp24 will beturned off and solenoid 64 de-energized to return switch 22 to theposition shown.

When positive original 44 is to be projected, support 38 must bepositioned as shown in solid lines in FIG. 1 against stop 68 with thepositive original in position to close switch 70 which isconnected topotential source 72 to provide a signal to one input of AND gate 74. Asecond signal is provided to another input of AND gate 74 from switch 58which is closed by engagement with support 38 and a third signal andfinal signal is provided to a third input to AND gate 74 when printbutton 54 is closed whereupon AND gate 74 is enabled to provide a signalto single shot 76. Single shot 76 provides an output signal ofpredetermined length to OR gate 66 which is enabled to energize lamp 24and project the image of positive original 44 through dichroic mirror10, photoconductive-liquid crystal sandwich S, and field lens 26 ontocharged photoconductive surface 34 to form a positive electrostaticlatent image thereon which may be utilized in a conventional manner.During the projection of an image from positive original 44, ultravioletlamp 6 is not energized and no potential is applied across thephotoconductive-liquid crystal sandwich S so that the liquid crystallayer remains in its quiescent or transparent state and thereforepermits the image of positive image 44 to be projected therethrough.

It is readily apparent that apositive electrostatic latent image can beformed on photoconductive surface 34 from either a negative original ora positive original so that reverse development techniques need not beemployed for the development of the electrostatic latent image. Thus,uniform quality of prints from both negative originals and positiveoriginals can more nearly be maintained.

An alternative embodiment is shown in FIG. 2 wherein a negative original2'v is positioned by supports 4 so that an image thereof may beprojected by ultraviolet lamp 6' through a lens system 8' onto adichroic mirror 10', which reflects ultraviolet light but transmitswhite light. Thus, the negative image is projected ontophotoconductive-liquid crystal sandwich S which includes, in order, atransparent electrode 12, a photoconductive layer 14, a liquid crystallayer 16', and a second transparent electrode 18. Conveniently,potential source 20' may be applied across the electrodes by means ofswitch 22' to create an electrical field thereacross so that when theimage of negative original 2 is projected onto photoconductive surface14', the surface will act as if it is more conductive in the exposedareas to increase the field across liquid crystal layer 16 therebyforming a positive image therein which may be projected by means ofwhite light 24' through field lens 26, objective lens 28 and aperture 30to a pivotal plane mirror onto a photosensitive surface, such as acharged photoconductor 34' supported on a conductive base 36. Thus, theimage ofa negative original can be formed into a positive temporaryimage on the photoconductive-liquid crystal sandwich structure and thispositive image can be projected onto a charged photoconductive surface34' to form a positve electrostatic latent image which can be developedby conventional techniques.

In this embodiment, if a copy is to be made of a positive original, theoriginal 86 is supported, as by a transparent base 88 for illumination,as by white light sources 90, so that the positive image thereof isprojected through lens system 92 onto charged photoconductive surface 34when plane mirror 80 is pivoted to the dotted line position.

Circuit logic which can be used for controlling this apparatus isillustrated. When a negative original is positioned, as shown in FIG. 2,switch 93 which is connected to potential source 94 will be closedproviding a signal to one input of AND gate 96. A second signal to asecond input of AND gate 96 will be provided by switch 98 from potentialsource 100 which switch 98 is engaged by pivotal plane mirror 80 in thesolid line position. A third and final input signal to AND gate 96 isprovided when print button 102, which is connected to potential source104, is closed. Whe these conditions are met, AND gate 96 is enabled toprovide a signal to single shot 106 which in turn provides a signal ofapredetermined time duration which energizes ultraviolet light 6 toproject the image of the negative original onto photoconductive-liquidcrystal sandwich S and at the same time energizes solenoid 108 to closeswitch 22' to create 'a field between electrodes 12 and 18'. This samesignal from single shot 106 also energizes lamp 24 so that the temporaryimage thus formed on the photoconductive-liquid crystal sandwich will beprojected so as to be reflected by plane mirror 80 onto chargedphotoconductive surface 34' to form a positive electrostatic latentimage.

When an image of positive original 86 is to be projected, switch 110,connected to potential source 112, is closed to provide an input signalto AND gate 114. A second input to AND gate 114 is provided when mirror80 is in the dotted line position to close switch 116, connected topotential source 118. The third and final input to AND gate 114 isprovided when the operator closes print button 102 thereby enabling ANDgate 114 to provide a signal to single shot 120 which in turn provides asignal of a predetermined time duration to energize lamps 90 therebyprojecting an image of original 86 onto charged photoconductive surface34' to provide a positive electrostatic latent image which may bedeveloped or otherwise used in a conventional manner. Of course, meansnot shows, may be provided in each instance to vary the exposure time inaccordance with the density and contrast of the original.

If desired, a liquid crystal material having a memory, such as a mixtureof nematic and cholesteric mesophases, can be used in the embodiments ofFIGS. 1 and 2, in which case, both light sources may provide radiationof the same wavelength. An image of the original is projected, by onelight source, onto the sandwich structure while a potential is appliedacross the electrodes to form a temporary image. After the potential isremoved, the temporary image is projected by the other light source ontothe photosensitive material.

A suitable liquid crystal material is a mixture of a nematic mesophase,such as N-[p-Methoxybenzylidene]- p-Butylaniline and a cholestericmesophase of cholesteryl oleyl carbonate, wherein the mixture is partsby weight of nematic mesophase to one part cholesteric mesophase. Thephotoconductive material can be 4, 4'-diethylamino-2,2-dimethyltriphenol methane and a polycarbonate resin together with apyrylium dye prepared as in Example I of British Patent 1,153,506 issued Sept. 29, 1969.

A low cost exposure station is illustrated in FIG. 3 for use with amemory type liquid crystal which requires only one exposure lamp. Inthis embodiment, a negative original 2", is positioned, as by suport 4"so that an image thereof may be projected by lamp 6" along an opticalpath through objective lens 8" onto sandwich structure S" which includesin order: a first transparent electrode 12, a photoconductive layer 14',a liquid crystal layer 16 and a second transparent electrode 18". Areverse or positive temporary image is formed in the liquid crystallayer, after which the original is removed from the optical path and thetemporary image is projected by lamp 6" through field lens 26" andobjective lens 23" at aperture 30" onto a photosensitive surface, suchas charged photoconductive surface 34" on a conductive backing 36", toform a positive electrostatic latent image. A positive original can alsobe positioned by support 4 to be projected through sandwich structure 5"which is maintained in a transparent condition so that the image of theoriginal is projected therethrough the sandwich structure and directlyonto photoconductive surface 34 to form a positive electrostatic latentimage.

When negative original 2" is positioned, as shown, by the operatorswitch 124 which is connected to a power source 126 will be closed toprovide a signal to one input of each of AND gates 128, 130 and 132 andto NAND gate 134. The operator then closes switch 136 against terminal Nso that a signal is provided from power source 138 to the second andfinal input of AND gate 132. This causes AND gate 132 to be enabled andprovide a signal to single shot 140 which in turn sets flip-flop 142 sothat it provides a signal from its one terminal to a second input of ANDgate 128 and to input of OR gate 144 which is enabled to energize lamp6". At the same time the signal from single shot 140, energizes solenoid146 to close switch 148 to connect d.c. potential source 150 acrosselectrodes 12" and 18". The signal from single shot is also provided tothe second and final input of NAND gate 134. Thus, photoconductive layer14" is exposed to an image of negative original 2" to form a temporaryreverse image on liquid crystal layer 16" while potential is appliedacross the electrodes. Upon termination of the signal from single shot1140, switch 148 returns to its normally open position shown in FIG. 3and the positive temporary image on liquid crystal layer 16" will bestored thereon. The operator then removes original 2" from the opticalpath so that light 6" projects the positive temporary image onto chargedphotoconductive surface 34". Upon removal of the original, switch 124 isopened enabling NAND gate 134, which in turn enables single shot 152 toenable OR gate 154 and solenoid 156 to open shutter 158 for apredetermined exposure time thereby forming a positive electrostaticlatent image on photoconductive surface 34". The output of single shot152 is also connected to AND gate 128 which is enabled when this signalis terminated, upon completion of the exposure, to enable single shot160 and energize solenoid 162. This positions switch 148 to apply a.c.potential source 164 across electrodes 12" and 18" to erase thetemporary image on liquid crystal layer 16. Upon termination of thesignal from single shot 160, switch 148 returns to its intermediate openposition, as shown. The signal from single shot 160 also clearsflip-flop 142 so that the circuit is in proper state for exposing asubsequent charged photoconductive surface to another original.

When a positive original is positioned in the optical path in theposition previously occupied by negative original 2", the operatorcloses swwtch 136 against the terminal P so that an input signal isprovided from potential source 138 to one input of AND gate 130 whosesecond and final input is provided from potential source 126 by closedswitch 124. This enables AND gate 130 which then enables single shot 166to provide a signal to OR gate 144 to illuminate lamp 6" and alsoprovides a signal to OR gate 154 to energize solenoid 156 to openshutter 158. Since switch 148 remains in its intermediate position sothat no potential is applied across electrodes 12" and 18", no image isformed on liquid crystal layer 16" and photoconductive-liquid crystalsandwich S" remain transparent and transmits the image from the positiveoriginal to charged photoconductive surface 34 to form a positiveelectrostatic latent image.

If desired, lamp 6" can be replaced with two separate light sources ofdifferent intensities or means (not shown) can be provided to adjust theintensity of lamp 6".

From the foregoing, the advantages of this invention are readilyapparent. An exposure station has been provided wherein a positiveelectrostatic image can be formed from either a positive or negativeoriginal thereby eliminating the necessity of developing one of theimages by reverse development techniques. In the embodiment of FIG. 1, atemporary image is formed on a photoconductive-liquid crystal sandwichby projecting an image of a negative original by ultraviolet light andthen projecting, by means of white light, the temporary image thusformed in the liquid crystal layer onto a charged photoconductivesurface to form a positive electrostatic latent image. A positiveoriginal is projected by means of the same white light source whichprojects the image through the photoconductive liquid crystal sandwich,when the sandwich is in the quiescent or transparent state, onto thecharged photoconductive surface to once again form a positiveelectrostatic latent image.

In the embodiment of FIG. 2 a negative original image is projected as inFIG. I to form a temporary positive image in the liquid crystal layerwhich in turn is projected by a white light onto a chargedphotoconductive surface to form a positive electrostatic latent image. Apositive original is projected through a lens system directly onto acharged photoconductive surface, without passing through thephotoconductiveliquid crystal sandwich to form a positive electrostaticlatent image.

In the embodiment of FIG. 3, a single mount is required for both anegative and a positive original and a single light source can be used,if desired, to form the temporary image and to expose a photosensitivesurface to the temporary image.

It will be understood that different circuitry could be used than thatdisclosed and that in the various embodiments and the photoconductivelayer of the liquid crystal sandwich structures could be sensitive to adifferent range of the electromagnetic spectrum and that anotherdifferent portion of the electromagnetic spectrum could be used toproject a temporary image rather than the visible or white light rangedescribed so long as the photosensitive surface upon which a latentimage is to be made is sensitive to the particular portion of theelectromagnetic spectrum which is used to project the image onto thecharged photoconductive surface.

Standard logic symbols have been used herein as disclosed in AmericanStandard Graphic Symbols For Logic Diagrams (ASA Y32.l41962), publishedby the American Institute of Electrical Engineers.

The invention has been described in detail with reference to preferredembodiments thereof, but it will be understood that variations andmodifications can be effected within the spirit and scope of theinvention.

I claim:

1. Apparatus for forming a latent image on a photosensitive surface fromeither a first original or a second original, which is the reverse ofthe first original, wherein the latent image of the first original isreversed and the latent image of the second original is the same as thesecond original, said paparatus comprising:

means for supporting the photosensitive surface for exposure;

means for forming a temporary image which is the reverse of the firstoriginal image in response to exposure to a radiation patterncorresponding to the first original image; means for supporting thefirst and second originals; means for exposing said temporary imageforming means to a radiation pattern corresponding to the first originalto form said reverse temporary image;

means for projecting radiation through said reverse temporary image toexpose the photosensitive surface to form a latent image thereon whichis the reverse of the first original; means for exposing thephotosensitive surface to an image of the second original to form alatent image which is the same as the second original; and

means for selectively forming a latent image from either the firstoriginal or the second original.

2. An apparatus, as claimed in claim 1, wherein said temporary imageforming means includes:

a liquid crystal layer in which said temporary image is formed; meansfor applying an electric field across said liquid crystal layer; and 5means for varying said electric field across said liquid crystal layerin response to exposure of said temporary image forming means to saidradiation pattern to form said reverse temporary image in said liquidcrystal layer.

3. An apparatus, as claimed in claim 2, wherein said means to vary theelectric field includes:

a photoconductive layer adjacent said liquid crystal layer; wherein saidmeans for forming a radiation pattern corresponding to an image of thefirst original includes:

a first source of radiation; and wherein said means for forming saidtemporary image includes:

a second source of radiation.

4. An apparatus for forming a latent image on a photosensitive surfacefrom either a first original or a second original, which is the reverseof the first original, wherein the latent image of the first original isreversed and the latent image of the second original is the same as thesecond original, said apparatus comprising:

means for supporting the photosensitive surface for exposure:

a layered sandwich structure which includes in order:

a first transparent electrode;

a photoconductive layer;

a liquid crystal layer; and

a second transparent electrode;

means for applying a potential between said electrodes; means forsupporting the first original; means for exposing said photoconductivelayer to an image of the first original when said potential is appliedacross said electrodes to increase the electric field across portions ofsaid liquid crystal layer corresponding to exposed portions of saidphotoconductive layer to form a reverse temporary image in said liquidcrystal layer; means for projecting radiation through said layeredsandwich structure to expose the photoconductive surface to said reversetemporary image to form a latent image on the photosensitive surfacewhich is the reverse of said first original; means for supporting thesecond original; means for exposing the photosensitive surface to animage of the second original to form a corresponding latent image on thephotosensitive surface; and

means for selectively forming a latent image from ei ther the firstoriginal or the second original.

5. An exposure station for forming a positive electrostatic latent imageon a charged photoconductive surface from either a positive original ora negative original, said exposure station comprising:

means for supporting the charged photoconductive surface for exposure;

a layered sandwich structure which includes in order:

a first transparent electrode;

a photoconductive layer;

a liquid crystal layer; and

a second transparent electrode;

means for applying a potential between said electrodes;

means for supporting the negative original;

first means for exposing the photoconductive layer to an image of thenegative original when said potential is applied across said electrodesto increase the electric field across portions of said liquid crystallayer corresponding to exposed portions of said photoconductive layer toform a positive temporary image in said liquid crystal layer;

first image projecting means for projecting radiation along a projectionpath through said layered sandwich structure to expose the chargedphotoconductive surface to said positive temporary image to form acorresponding positive electrostatic latent image on the photoconductivesurface;

means for supporting the positive original;

second image projecting means for projecting radiation along a path forexposing the charged photoconductive surface to the image of saidpositive original to form a corresponding positive electrostatic latentimage on the photoconductive surface; and

means for selectively enabling either said first image projecting meansor said second image projecting means.

6. An exposure station, as claimed in claim 5, wherein said means forexposing the charged photoconductive surface to said positive originalincludes:

said first radiation projecting means; and

said positive original supporting means.

7. An exposure station as claimed in claim 6, wherin said means forexposing the charged photoconductive surface to said positive originalfurther includes:

means mounting said positive original supporting means for movement froma first position along said projection path and between said radiationprojecting means and said layered sandwich structure. for projecting theimage of the positive original through said sandwich structure to exposethe charged photoconductive surface to said positive original, and asecond position spaced from said optical path wherein said radiationprojecting means is usable to expose the charged photoconductive surfaceto said positive temporary image.

8. An exposure station, as claimed in claim 5,-

wherein said means for exposing the charged photoconductive surface toan image of the positive original includes:

second means for projecting radiation to form the corresponding positiveelectrostatic latent image on the charged photoconductive surface.

9. An exposure station, as claimed in claim 8, wherein said means forexposing the charged photoconductive surface to an image of a positiveoriginal further includes:

a plane mirror pivotal from a first position for reflecting a radiationpattern from one of said temporary image and the positive original ontosaid charged photoconductive surface to a second position wherein aradiation pattern from the other of said temporary image and thepositive original is projectable directly onto said chargedphotoconductive surface without being reflected from said mirror.

10. An exposure station for forming a positive electrostatic latentimage on a charged photoconductive surface from either a positiveoriginal or a negative original, said exposure station comprising:

means for supporting the charged photoconductive surface for exposure;

a layered sandwich structure which includes in order:

a first transparent electrode;

a photoconductive layer which is responsive only to the ultravioletportion of the electromagnetic spectrum;

a liquid crystal layer; and

a second transparent electrode;

means for applying a potential between said electrodes;

means for supporting the negative original;

a source of ultraviolet light for projecting an image of the negativeoriginal along an optical path onto said photoconductive layer when saidpotential is applied across said electrodes to render exposed areas ofsaid photoconductive layer more conductive than unexposed areas thereofto form a positive temporary image on said liquid crystal layer;

a dichroic mirror for reflecting ultraviolet light and transmittingwhite light positioned along said optical path to reflect said negativeimage projected by said ultraviolet light onto said photoconductivelayer;

a source of white light positioned to be projected along a projectionpath through said dichroic mirror and said sandwich structure to exposesaid charged photoconductive Surface to said temporary image to form acorresponding positive electrostatic latent image on saidphotoconductive surface; and

means for supporting the positive original movable from a first positionalong said projection path and between said white light source and saiddichroic mirror, for projecting an image of the positive originalthrough said dichroic mirror and said sandwich structure to expose saidcharged photoconductive surface to an image of the positive original toform a corresponding positive electrostatic latent image on saidphotoconductive surface, to a second position spaced from saidprojection path for projecting said temporary image.

11. An exposure station, as claimed in claim 10,

wherein said movable supporting means includes:

lens means for projecting an image of the positive original.

12. An exposure station, as claimed in claim 10, further including:

means for enabling said ultraviolet light source and said white lightsource and for applying said potential across said electrodes when anegative original is supported by said negative original supportingmeans and said positive original supporting means is in said secondposition and for enabling said white light source and disabling saidultraviolet light source and said potential applying means when saidmeans for supporting said positive original is in said first positionand a positive original is supported thereby.

13. An exposure station for forming a positive electrostatic latentimage on a charged photoconductive surface from either a positiveoriginal or a negative original, said exposure station comprising:

means for supporting the charged photoconductive surface for exposure;

a layered sandwich structure which includes in order:

a first transparent electrode;

a photoconductive layer which is responsive only to the ultravioletportion of the electromagnetic spectrum;

a liquid crystal layer; and

a second transparent electrode;

means for applying a potential between said electrodes;

means for supporting a negative original;

a source of ultraviolet light for projecting an image of the negativeoriginal onto said photoconductive layer when said potenital is appliedacross said electrodes to render exposed areas of said photoconductivelayer more conductive than unexposed areas thereof to form a positivetemporary image on said liquid crystal layer;

a first source of white light for projecting said temporary image alongan optical path to expose the charged photoconductive surface to saidtemporary image to form a corresponding positive electrostatic latentimage on the photoconductive surface;

a plane mirror movable from a first position along said optical path,for reflecting said positive temporary image projected by said firstwhite light source onto the charged photoconductive surface, to a secondposition spaced from said optical path;

means for supporting the positive original; and

a second source of white light for projecting an image of the positiveoriginal onto the charged photoconductive surface when said plane mirroris in said second position.

14. An exposure station, as claimed in claim 13, further including:

means for enabling said ultraviolet light source and said first whitelight source and for applying said potential across said electrodes andfor disabling said second white light source when a negative original issupported by said negative original supporting means and said planemirror is in said first position and for enabling said second whitelight source and for disabling said first white light source when apositive original is supported by said positive original supportingmeans and said plane mirror is in siad second position.

15. Apparatus for forming a latent image onva photosensitive surfacefrom either a first original or a second original, which is the reverseof the first original, wherein the latent image of the first original isreversed and the latent image of the second original is the same as thesecond original, said apparatus comprising:

means for supporting the photosensitive surface for exposure; a layeredsandwich structure which includes in order:

a first transparent electrode; a photoconductive layer; a liquid crystallayer of the type having the capacity to store an image at leasttemporarily; and a second transparent electrode; means for applying afirst potential between said electrodes during formation of a temporaryimage in said liquid crystal layer;

means for applying a second potential between said electrodes to erasesaid temporary image;

means for supporting either said first original or said second original;

means for projecting illumination;

first control means to sequentially: enable said first potentialapplying means and said illumination means when the first original is insaid supporting means to expose said photoconductive layer to a patternof radiation corresponding to said first original to form said reversetemporary image in said liquid crystal layer; disables said firstpotential applying means when the first original is removed from saidsupporting means and expose said photosensitive surface to said reversetemporary image for a predetermined time to form a latent imagecorresponding to said reverse temporary image; and enable said secondpotential applying means to erase said reverse temporary image afterexposure of said photosensitive surface to said temporary image;

second control means to enable said illumination means when the secondoriginal is in said supporting means to expose the photosensitivesurface to a radiation pattern corresponding to said second original toform a latent image corresponding to said second original; and

means for selectively enabling either said first control means or saidsecond control means.

16. An exposure station for forming a positive electrostatic latentimage on a charged photoconductive surface from either a positiveoriginal or a negative original, said exposure station comprising:

means for supporting the charged photoconductive surface for exposure; alayered sandwich structure which includes in order:

a first transparent electrode; a photoconductive layer; a liquid crystallayer of the type having the capacity to store an image at leasttemporarily; and

a second transparent electrode;

means for applying a first potential between said electrodes duringformation of a temporary image in said liquid crystal layer;

means for applying a second potential between said electrodes to erasesaid temporary image;

means for supporting either said first original or said second original;

means for projecting illumination;

first control means to sequentially: enable said first potentialapplying means and said illumination means when said negative originalis in said supporting means to expose said photoconductive layer to animage'of said negative original projected along an optical path to formsaid positive temporary image in said liquid crystal layer; disable saidfirst potential applying means when the negative original is removedfrom said supporting means and project said positive temporary imageinto said charged photoconductive surface for a predetermined time toform a positive electrostatic latent image; and enable said secondpotential applying means to erase said positive temporary image afterexposure of said photoconductive surface to said temporary image;

second control means to enable said illumination means when the positiveoriginal is in said supporting means to expose the chargedphotoconductive surface for a predetermined period of time to an imageof said positive original projected along said optical path and throughsaid layered sandwich structure by said illumination means and to form a16 liquid crystal layer comprises:

a mixture of nematic and cholesteric liquid crystal materials.

2. An apparatus, as claimed in claim 1, wherein said temporary imageforming means includes: a liquid crystal layer in which said temporaryimage is formed; means for applying an electric field across said liquidcrystal layer; and means for varying said electric field across saidliquid crystal layer in response to exposure of said temporary imageforming means to said radiation pattern to form said reverse temporaryimage in said liquid crystal layer.
 3. An apparatus, as claimed in claim2, wherein said means to vary the electric field includes: aphotoconductive layer adjacent said liquid crystal layer; wherein saidmeans for forming a radiation pattern corresponding to an image of thefirst original includes: a first source of radiation; and wherein saidmeans for forming said temporary image includes: a second source ofradiation.
 4. An apparatus for forming a latent image on aphotosensitive surface from either a first original or a secondoriginal, which is the reverse of the first original, wherein the latentimage of the first original is reversed and the latent image of thesecond original is the same as the second original, said apparatuscomprising: means for supporting the photosensitive surface forexposure: a layered sandwich structure which includes in order: a firsttransparent electrode; a photoconductive layer; a liquid crystal layer;and a second transparent electrode; means for applying a potentialbetween said electrodes; means for supporting the first original; meansfor exposing said photoconductive layer to an image of the firstoriginal when said potential is applied across said electrodes toincrease the electric field across portions of said liquid crystal layercorresponding to exposed portions of said photoconductive layer to forma reverse temporary image in said liquid crystal layer; means forprojecting radiation through said layered sandwich structure to exposethe photoconductive surface to said reverse temporary image to form alatent image on the photosensitive surface which is the reverse of saidfirst original; means for supporting the second original; means forexposing the photosensitive surface to an image of the second originalto form a corresponding latent image on the photosensitive surface; andmeans for selectively forming a latent image from either the firstoriginal or the second original.
 5. An exposure station for forming apositive electrostatic latent image on a charged photoconductive surfacefrom either a positive original or a negative original, said exposurestation comprising: means for supporting the charged photoconductivesurface for exposure; a layered sandwich structure which includes inorder: a first transparent electrode; a photoconductive layer; a liquidcrystal layer; and a second transparent electrode; means for applying apotential between said electrodes; means for supporting the negativeoriginal; first means for exposing the photoconductive layer to an imageof the negative original when said potential is applied across saidelectrodes to increase the electric field across portions of said liquidcrystal layer corresponding to exposed portions of said photoconductivelayer to form a positive temporary image in said liquid crystal layer;first image projecting means for projecting radiation along a projectionpath through said layered sandwich structure to expose the chargedphotoconductive surface to said positive temporary image to form acorresponding positive electrostatic latent image on the photoconductivesurface; means for supporting the positive original; second imageprojecting means for projecting radiation along a path for exposing thecharged photoconductive surface to the image of said positive originalto form a corresponding positive electrostatic latent image on thephotoconductive surface; and means for selectively enabling either saidfirst image projecting means or said second image projecting means. 6.An exposure station, as claimed in claim 5, wherein said means forexposing the charged photoconductive surface to said positive originalincludes: said first radiation projecting means; and said positiveoriginal supporting means.
 7. An exposure station as claimed in claim 6,wherin said means for exposing the charged photoconductive surface tosaid positive original further includes: means mounting said positiveoriginal supporting means for movement from a first position along saidprojection path and between said radiation projecting means and saidlayered sandwich structure, for projecting the image of the positiveoriginal through said sandwich structure to expose the chargedphotoconductive surface to said positive original, and a second positionspaced from said optical path wherein said radiation projecting means isusable to expose the charged photoconductive surface to said positivetemporary image.
 8. An exposure station, as claimed in claim 5, whereinsaid means for exposing the charged photoconductive surface to an imageof the positive original includes: second means for projecting radiationto form the corresponding positive electrostatic latent image on thecharged photoconductive surface.
 9. An exposure station, as claimed inclaim 8, wherein said means for exposing the charged photoconductivesurface to an image of a positive original further includes: a planemirror pivotal from a first position for reflecting a radiation patternfrom one of said temporary image and the positive original onto saidcharged photoconductive surface to a second position wherein a radiationpattern from the other of said temporary image and the positive originalis projectable directly onto said charged photoconductive surfacewithout being reflected from said mirror.
 10. An exposure station forforming a positive electrostatic latent image on a chargedphotoconductive surface from either a positive original or a negativeoriginal, said exposure station comprising: means for supporting thecharged photoconductive surface for exposure; a layered sandwichstructure which includes in order: a first transparent electrode; aphotoconductive layer which is responsive only to the ultravioletportion of the electromagnetic spectrum; a liquid crystal layer; and asecond transparent electrode; meAns for applying a potential betweensaid electrodes; means for supporting the negative original; a source ofultraviolet light for projecting an image of the negative original alongan optical path onto said photoconductive layer when said potential isapplied across said electrodes to render exposed areas of saidphotoconductive layer more conductive than unexposed areas thereof toform a positive temporary image on said liquid crystal layer; a dichroicmirror for reflecting ultraviolet light and transmitting white lightpositioned along said optical path to reflect said negative imageprojected by said ultraviolet light onto said photoconductive layer; asource of white light positioned to be projected along a projection paththrough said dichroic mirror and said sandwich structure to expose saidcharged photoconductive surface to said temporary image to form acorresponding positive electrostatic latent image on saidphotoconductive surface; and means for supporting the positive originalmovable from a first position along said projection path and betweensaid white light source and said dichroic mirror, for projecting animage of the positive original through said dichroic mirror and saidsandwich structure to expose said charged photoconductive surface to animage of the positive original to form a corresponding positiveelectrostatic latent image on said photoconductive surface, to a secondposition spaced from said projection path for projecting said temporaryimage.
 11. An exposure station, as claimed in claim 10, wherein saidmovable supporting means includes: lens means for projecting an image ofthe positive original.
 12. An exposure station, as claimed in claim 10,further including: means for enabling said ultraviolet light source andsaid white light source and for applying said potential across saidelectrodes when a negative original is supported by said negativeoriginal supporting means and said positive original supporting means isin said second position and for enabling said white light source anddisabling said ultraviolet light source and said potential applyingmeans when said means for supporting said positive original is in saidfirst position and a positive original is supported thereby.
 13. Anexposure station for forming a positive electrostatic latent image on acharged photoconductive surface from either a positive original or anegative original, said exposure station comprising: means forsupporting the charged photoconductive surface for exposure; a layeredsandwich structure which includes in order: a first transparentelectrode; a photoconductive layer which is responsive only to theultraviolet portion of the electromagnetic spectrum; a liquid crystallayer; and a second transparent electrode; means for applying apotential between said electrodes; means for supporting a negativeoriginal; a source of ultraviolet light for projecting an image of thenegative original onto said photoconductive layer when said potenital isapplied across said electrodes to render exposed areas of saidphotoconductive layer more conductive than unexposed areas thereof toform a positive temporary image on said liquid crystal layer; a firstsource of white light for projecting said temporary image along anoptical path to expose the charged photoconductive surface to saidtemporary image to form a corresponding positive electrostatic latentimage on the photoconductive surface; a plane mirror movable from afirst position along said optical path, for reflecting said positivetemporary image projected by said first white light source onto thecharged photoconductive surface, to a second position spaced from saidoptical path; means for supporting the positive original; and a secondsource of white light for projecting an image of the positive originalonto the charged photoconductive surface when said plane mirror is insaid second position.
 14. An exposurE station, as claimed in claim 13,further including: means for enabling said ultraviolet light source andsaid first white light source and for applying said potential acrosssaid electrodes and for disabling said second white light source when anegative original is supported by said negative original supportingmeans and said plane mirror is in said first position and for enablingsaid second white light source and for disabling said first white lightsource when a positive original is supported by said positive originalsupporting means and said plane mirror is in siad second position. 15.Apparatus for forming a latent image on a photosensitive surface fromeither a first original or a second original, which is the reverse ofthe first original, wherein the latent image of the first original isreversed and the latent image of the second original is the same as thesecond original, said apparatus comprising: means for supporting thephotosensitive surface for exposure; a layered sandwich structure whichincludes in order: a first transparent electrode; a photoconductivelayer; a liquid crystal layer of the type having the capacity to storean image at least temporarily; and a second transparent electrode; meansfor applying a first potential between said electrodes during formationof a temporary image in said liquid crystal layer; means for applying asecond potential between said electrodes to erase said temporary image;means for supporting either said first original or said second original;means for projecting illumination; first control means to sequentially:enable said first potential applying means and said illumination meanswhen the first original is in said supporting means to expose saidphotoconductive layer to a pattern of radiation corresponding to saidfirst original to form said reverse temporary image in said liquidcrystal layer; disables said first potential applying means when thefirst original is removed from said supporting means and expose saidphotosensitive surface to said reverse temporary image for apredetermined time to form a latent image corresponding to said reversetemporary image; and enable said second potential applying means toerase said reverse temporary image after exposure of said photosensitivesurface to said temporary image; second control means to enable saidillumination means when the second original is in said supporting meansto expose the photosensitive surface to a radiation patterncorresponding to said second original to form a latent imagecorresponding to said second original; and means for selectivelyenabling either said first control means or said second control means.16. An exposure station for forming a positive electrostatic latentimage on a charged photoconductive surface from either a positiveoriginal or a negative original, said exposure station comprising: meansfor supporting the charged photoconductive surface for exposure; alayered sandwich structure which includes in order: a first transparentelectrode; a photoconductive layer; a liquid crystal layer of the typehaving the capacity to store an image at least temporarily; and a secondtransparent electrode; means for applying a first potential between saidelectrodes during formation of a temporary image in said liquid crystallayer; means for applying a second potential between said electrodes toerase said temporary image; means for supporting either said firstoriginal or said second original; means for projecting illumination;first control means to sequentially: enable said first potentialapplying means and said illumination means when said negative originalis in said supporting means to expose said photoconductive layer to animage of said negative original projected along an optical path to formsaid positive temporary image in said liquid crystal layer; disable saidfirst potential applying means when the nEgative original is removedfrom said supporting means and project said positive temporary imageinto said charged photoconductive surface for a predetermined time toform a positive electrostatic latent image; and enable said secondpotential applying means to erase said positive temporary image afterexposure of said photoconductive surface to said temporary image; secondcontrol means to enable said illumination means when the positiveoriginal is in said supporting means to expose the chargedphotoconductive surface for a predetermined period of time to an imageof said positive original projected along said optical path and throughsaid layered sandwich structure by said illumination means and to form apositive electrostatic latent image on said photoconductive surface; andmeans for selectively enabling either said first control means or saidsecond control means.
 17. Apparatus, as claimed in claim 16, whereinsaid liquid crystal layer comprises: a mixture of nematic andcholesteric liquid crystal materials.